This invention relates to the control of a printing apparatus of the type in which image information is decomposed into a set of dots (or a dot pattern) in a image memory before printout, such as a laser beam printer, and more specifically to the control of the decomposition of image information in memories and printout therefrom.
A prior art printing apparatus disclosed in U.S. Pat. No. 4,125,829 decomposes character information and format information separately into respective dot patterns which are stored in respective memories and are superimposed at the time of printout. This apparatus operates in the scan line by scan line fashion, that is, it decomposes image information for a scan line and prints it out, then for the next scan line, and so on.
As a prior improvement aiming at speedup, there has been an printing apparatus which is equipped with a couple of memories each of which accommodates dot patterns for a complete page so that dot patterns for a page are read out from one of the memories to be supplied to a printer while dot patterns for the next page are being developed in the other memory. As is often the case, an image to be printed consists of a portion for a format and a portion for characters, diagrams and the like to fill in the format, the latter portion carrying the significant part of information. It is also usual that a format is kept intact over a pluraity of pages. Nevertheless it is conventional to decompose a format into dots anew for every page. As a result, when a complicated format is used, the decomposition of format portion fails to catch up with printout, and in spite of the installation of the above-mentioned couple of memories the waiting time of a printer becomes long, resulting in a delay in printing.